Restoration strategies for radioactively contaminated sites and their close surroundings

Technical Annex

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A lot of nuclear facilities in Europe reached the end of their as designed life expectancy. While the main technical part of the installations will be subject to a controlled decommissioning, in many cases contamination has been dispersed over the site or is contained by methods presenting only a weak reliability for long-term storage. The clean-up of those parts of the sites by conventional techniques is very expensive and may be very questionable on the basis of cost-benefit evaluations. Those problems are well-known e.g. by the large clean-up programmes of former military sites in the U.S. and will become urgent when decisions have to be taken about the future of sites as well in Eastern as in Western Europe. The U.S.-experience shows that the application of alternative techniques, e.g. in-situ remediation is hampered by the lack of transparent risk assessments, considering the exposure of the present and future populations and of the workers.

The main objective of this coordinated project is to develop a generic methodology for ranking of restoration techniques as a function of site (and contamination) characteristics. A manual will be produced in which this methodology is explained and applied to major classes of site restoration cases. All relevant data will be reviewed and documented, important sources of uncertainty identified and to the extent possible uncertainties will be reduced.

The development of the generic methodology will be based on an analysis of existing remediation methodologies and contaminated sites, and will be structured in following steps:


The overall project is broken down into working packages. For performing the tasks in the working packages a phased approach is followed, with transfers of information/data between the working packages at regular time intervals (mainly at the end of phases).

WP1X: Case Studies

Four specific contaminated sites will be studied in detail:

They are representative of four major classes. The former two are related to solid sources of contamination (wastes), namely:

The latter two are related to liquid sources of contamination (wastes), namely:

Phase 1: Documentation of cases

The objective of phase 1 is the characterization of the sites in view of the quantification of the parameters to be introduced in the risk assessment model developed in WP4 and in the selection procedure of restoration techniques (developed in WP5).

Each of the sites will be located on geographical maps and the contaminated surface area indicated.

Human activities on the site (close surroundings) that may determine or influence human exposure will be documented:

Fundamental climatologic and meteorologic characteristics of the site are important as they will determine the soil water balance. Statistics on precipitation, wind velocity, wind direction, temperature and solar radiation will be supplied over at least 10 recent years. The concentrations of radionuclides are to be given as a function of the location and the chemical composition is to be indicated (if possible).

For the solid contamination sources (WP11, WP12)

The depth of the contaminated layers and the concentration of the radionuclides as a function of depth as well as the total inventories will be indicated.

The surface soils will be characterized as to the:

The geo-hydrological characteristics of the site will be given:

Surface waters in the environment, relevant in terms of radiological impact will be identified, and following characteristics determined:

For the liquid contamination sources (WP13, WP14)

The characteristics relating to surface waters, indicated above, will be determined in the sections relevant for the exposure of man.

The characteristics of the sediment, influencing the sorption or mobility of the radionuclides will also be indicated:

Phase 2: Assessment of Restoration Techniques

In this phase the risk assessment model developed in WP4 and the criteria developed for ranking restoration techniques in WP5 will be applied to the combinations of cases and possibly relevant restoration techniques.

The objectives are to demonstrate the applicability of the risk assessment model, to evaluate the performances of restoration techniques for specific cases and to formulate generic conclusions concerning the selection of restoration techniques for the base cases, the sites are representative of.

For these purposes, scenarios applicable to each case will be developed:

The application of the risk assessment model will yield annual individual doses or radiological risks and collective doses or radiological risks, with and without the application of restoration techniques, in order to assess the radiological performance of those techniques.

Deterministic calculations and stochastic analyses will be carried out, the latter with the aim to estimate the robustness of the results.

Next to the radiological attributes determined above, attributes in the economical, technical and social fields will be assessed, according to the criteria in the ranking procedure for restoration options, developed in WP5.

Conclusions from the application of this procedure on the combinations of cases/restoration techniques, and that are of a generic nature for the base cases considered, will be introduced in WP6 as building blocks for the manual.

WP2: Physico-chemical phenomena

The objective of this working package is to characterize the main parameters determining the source term evolution with regard to their importance and availability for risk assessment models. The focus will be on physico-chemical phenomena governing the behaviour of radioactive substances in the near-field. The work in this working package will be carried out by Research Centre Rossendorf (RCR).

Phase 1: State-of-the-Art Description

The work in this phase will concentrate on the effects related to the aqueous path. The factors, that alter the release and the formation of distinct chemical species and ultimately the transport in many ways, include:

Based on the available literature (data compilations, chemical models, single papers and reviews, analogue case studies) an overview of the following parameters will be elaborated: stability constants for the possible aqueous complexes, solubility products for the solid phases, the rate laws governing their precipitation and dissolution, sorption parameters and retardation coefficients.

These parameters will be discussed in relation with their:

Ways will be investigated to reduce the parameter space to get simpler coefficients (probably functions of time and chemical composition) for the description of the source term evolution. These coefficients will then be incorporated into the risk assessment models developed in WP4.

Phase 2: Site-specific phenomena

In this phase, qualified estimates will be made to extract the phenomena expected to dominate the major classes of contaminated sites considered. Measurements will be made to fill the most critical holes in the relevant data framework. Giving a comprehensive description of the chemical composition of the aqueous phase and the mineral constituents of the solid matrix, the fractions available for transport will be modelled for each radionuclide. They will be calculated as a function of time, giving the necessary inputs for the application of the risk assessment model on the site classes.

Finally, this model will be applied to the test case sites of WP1X. This will allow a comparison of scenarios with different restoration strategies and give clues to the directions of further model refinement and extensions.

A general description of the source term evolution and conclusions about relevant parameter values for major classes of contaminated sites will be introduced in WP6 as building blocks for the manual.

WP3: Restoration techniques

The objective of this working package is

Phase 1: Identification

In phase 1 the possibly relevant restoration (remedial) techniques and sources of documentation on them, will be identified. The classes of techniques envisaged are

Physical techniques (removal and shielding of sources) will be examined by Studsvik (responsible) and SCK CEN in WP31. Chemical and biological treatments will be dealt with by WRI (responsible) and CRC in WP32. Besides own experiences, literature sources (NRC, EPA, IAEA, CEC, Conferences) will be divided between the participants for review according to the requirements specified in phase 2.

Phase 2: Characterization

In this phase characteristics of the restoration (remedial) techniques, related to their performance, economical costs, durability, life (of barrier) will be determined and quantified (where possible).

Characteristics related to the performance of the techniques depend on their aim:

Economical costs may consist of fixed costs and variable costs, related to the infrastructure needed, the consumables, labour volume.

Durability is essentially linked to barriers (to a lesser extent also to immobilization techniques). It will be expressed as resistance against mechanical, chemical and biological attacks, and against weathering (surface barriers). Where relevant the influence on the life of the barriers will be indicated.

Also secondary effects, problems with the manageability of the technique, will be mentioned.

Values of characteristics will be translated in parameter values or expressions for use in the risk assessment model (WP4) and in the ranking procedure of the restoration techniques (WP5). If only qualitative indications of characteristics are available, uncertainty ranges will be used where necessary.

Generic conclusions and relevant characteristics of the techniques with relation to the base cases considered will be introduced in WP6 as building stones for the manual.

WP4: Risk Assessment

The objective of this working package is to elaborate a risk assessment model enabling the evaluation of the radiological exposure of the general population due to the contamination of a site and the radiological exposure of intervention workers while performing restoration operations.

In a first phase, a generic deterministic model will be developed; in a second phase, case-specific modules and stochastic analyses will be provided for.

Phase 1: Development of a generic risk assessment model

A generic assessment methodology will have to consist of following steps:

The radiological quantities to be assessed are:

In principle it has been decided to start from an existing model, in casu BIOPATH (owner: Studsvik) to which necessary adaptations will be carried out by the owner, assisted by the other partners in WP4 (WRI and SCK CEN). Concerning the releases and transport of radionuclides in the near field, guidance will be available from WP2.

Phase 2: Case-specific adaptations

In the generic model developed in phase 1, at various steps adaptations or submodels (modules) will have to be provided in order to be able to apply the model to the cases considered. The adaptations required will be carried out by the partners responsible for the cases WP1X (WRI, Studsvik, SCK CEN).

Also in this phase, quantitative information concerning the influence of restoration techniques on parameters in the model will become available from WP3 and will be introduced by the partners responsible for WP3.1 (Studsvik) and WP3.2 (WRI).

Next to this, stochastic analysis software will be introduced or adapted in order to carry out uncertainty and sensitivity analyses.

The aim of these analyses is:

This will be carried out mainly by the owner of the model. If wanted, assistance will be given by the other partners of WP4 with software or programmes available.

After completion, the risk assessment model will be applied to the cases defined in WP1X (see WP1X - Phase 2). A general description of the methodology (model) will be made available for the manual (WP6)

WP5: Selection of restoration options

Among the possible restoration options or techniques applicable to a certain case, a ranking may be performed taking into account radiological, economical and social criteria.

Important radiological criteria are (as indicated in WP4):

Economic criteria include:

Social criteria may include:

The objectives of this working package is to define the criteria and attributes that are to be taken into account and to quantify them for the combinations of cases/restoration techniques considered. A methodology will be developed for ranking of restoration options for the base cases.

Phase 1: Review of criteria

In phase 1 a review of criteria applied on clean-up and restoration cases will be made up as a basis for defining criteria or attributes applicable to the base cases considered in our project. The developing international work (IAEA, ICRP, EU) will be included in this review.

The review will be carried out by RNL (Risoe National Laboratory).

Phase 2: Elaboration of a selection procedure

Firstly the applicable criteria and attributes for evaluating the combinations of the cases/restoration techniques will be defined.

Next criteria and attributes for combinations selected from a first rough screening will be quantified in order to be used in a multi-attribute analysis (Information from WP3 on restoration techniques will have to be made available).

Finally a methodology based on multi-attribute analysis will be elaborated, including the determination of preference values and weighing factors for the attributes, in order to rank combinations of cases/restoration options.

This methodology will be applied on the typical cases dealt with in WP1X.

Uncertainty analyses based on the uncertainty of important parameter values will indicate the degree of robustness of the results.

The general methodology for ranking restoration options in the base case will be introduced in WP6 for the elaboration of the manual.

Also the work in phase 2 will be carried out mainly by RNL. Assistance will be given by WRI for the drafting of the multi-attribute analysis programme.

WP6: The Manual

The objective of this working package is to elaborate a manual in which a general methodology is described for ranking or selecting restoration options for base cases, and in which general results and conclusions are shown.

The manual will be drafted by SCK CEN from contributions of the other partners in their capacity of responsible persons for the other working packages mentioned below. Special help will be provided by WRI with respect to the English language.

Phase 1: Basics

In this phase the description of the methodologies for risk assessment (WP4) and for ranking of restoration options (WP5) are introduced and the importance of physico-chemical phenomena in release and transport of radioactive substances (WP2) discussed.

Important features of restoration techniques in view of their evaluation will be indicated (WP3) and general conclusions on criteria and attributes collected.

Phase 2: Results

In this phase the general results of the applications of the methodologies above mentioned on the cases of WP1X are given and conclusions for the base cases drawn.

A generic ranking of relevant restoration techniques for the base cases will be shown and uncertainties indicated (reduced to the extent possible).

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